diff --git a/kern/sys_process.c b/kern/sys_process.c
--- a/kern/sys_process.c
+++ b/kern/sys_process.c
@@ -111,7 +111,7 @@
 
 	switch (uap->req) {
 	case PT_IO:
-		(void)copyout(&r.piod, uap->addr, sizeof r.piod);
+		error = copyout(&r.piod, uap->addr, sizeof r.piod);
 		break;
 	case PT_GETREGS:
 		error = copyout(&r.reg, uap->addr, sizeof r.reg);